Precision BioSciences and the University of North Carolina Gene Therapy Center are developing of a gene conversion technology for the permanent correction of disease- causing mutations in the human CFTR gene. This approach is based on the use of a double-strand DNA break to stimulate homologous recombination at the mutation site. Precision BioSciences has designed and biochemically characterized an engineered homing endonuclease which recognizes and cuts the dF508 allele of the CFTR gene. This designed enzyme is highly specific and able to discriminate the disease-causing allele from the healthy allele within a genomic background. A research plan is proposed to evaluate the ability of this enzyme to stimulate recombination at the dF508 mutation site and thereby correct the defect without any extraneous chromosomal modification. The designed endonuclease will first be optimized for intracellular function using a DNA-break reporter assay in a human cell line. The optimized endonuclease will then be used to repair the dF508 deletion in a dF508 cell line. If successful, this technology will enable the permanent and traceless in situ correction of dF508 to significantly enhance CF gene therapy strategies.Precision BioSciences and the University of North Carolina Gene Therapy Center are developing a method for the permanent cure of Cystic Fibrosis. This method involves directly repairing the DNA error that causes the disease. If we are successful, it will open the door for a new general technology for correcting genetic disorders. [unreadable] [unreadable] [unreadable]